Ultrasonic welders are known in the art, as exemplified by U.S. Pat. Nos. 5,772,100, 4,867,370 and 3,053,124. This class of devices utilizes ultrasonic energy to join metals, particularly nonferrous metals used in the electrical arts, as for example the splicing of wires and the attachment of a wire to a terminal. Ultrasonic welding is not actually “welding” in the sense that there is no application of heat as is used in conventional welding, wherein metals are heated to the point of melting into each other. In the case of ultrasonic welding, a mechanical vibration is applied to the metals, typically in the preferred frequencies of 20 kHz or 40 kHz.
The frequency and the amplitude of the vibration cause the metals to mutually gall at their contact surfaces. This galling results in contaminants, such as for example surface oxidation, to be displaced. The galling further causes the contact surfaces to be polished. As galling continues, the contact surfaces become intimate, whereupon atomic and molecular bonding occurs therebetween, thereby bonding the metals together with a weld-like efficacy (ergo, the term “ultrasonic welding”).
A number of considerations determine the efficacy of the metal-to-metal surface bond, the major considerations being the amplitude of the vibration, the applied force and the time of application. These variables collectively define the efficacy of bonding between the contacting metal surfaces. The applied power (P) is defined by the amplitude (X) of vibration times the force (F) applied normal to the metal surfaces (P=FX), and the applied energy (E) is defined by the applied power (P) times the time (t) of application (E=Pt). These variables are predetermined to achieve the most efficacious bond based upon the metals and the particular application.
To provide reliable and predictable bonds by ultrasonic welding, ultrasonic welders include power supplies and actuators controlled by a microprocessor. An example thereof is the “Ultraweld® 40” ultrasonic welder of AMTECH® (American Technology, Inc.) of Milford, Conn. This class of commercially available ultrasonic welders include: a power supply, a transducer where electrical energy is converted into mechanical vibration, an amplitude booster where the mechanical vibrations are amplified, and an output tool in the form of a horn which tunes the vibrations to a tip. The tip is aligned with a stationary anvil, and the ultrasonic welder includes one or more actuators which allow for movement of the tip relative to the anvil. Preferably, the tip and the anvil are knurled so as to grip the metals placed therebetween.
In operation of a conventional ultrasonic welder, a wire is stripped of its insulation jacket at an end section, and the stripped end section is then placed adjacent a top surface of a base of a terminal to which it is to be bonded. The operator places the stripped section of wire and terminal into the ultrasonic welder, such that the a bottom surface of the base rests upon the anvil and the stripped section of the wire is aligned with the tip. The operator then causes the sonic welder to automatically sequence.
A typical sequence for bonding a wire to a terminal may go as follows: the tip descends onto the stripped section of wire and applies a compressive force between it and the anvil (compressing the stripped section of wire onto the base of the terminal), the location of the tip relative to the anvil is sensed, and if within tolerances, the transducer is actuated so as to apply ultrasonic vibration to the tip for a preset time. Finally, the tip is retracted away from the stripped section of wire. The result is a bond of the stripped section of wire relative to the top surface of the base of the terminal in an area defined generally by the tip area.
While ultrasonic welding methodologies have advanced considerably in recent years. One advance is applying ultrasonic welding processes to insulation jacketed wires without firstly stripping them. A preferred acronym therefor is “UWTI” (Ultrasonic Welding Through Insulation).
As described in U.S. patent application Ser. No. 09/993,797, filed Nov. 24, 2001, and commonly owned by the assignee of the present application, the disclosure of which is hereby incorporated herein by reference, an insulation jacketed wire (multi-strand or single strand) with its insulation jacket thereon and intact is placed upon a top surface of a base of a terminal to which it is to be bonded and the staking wings of the terminal are stacked down onto the insulation jacketed wire. The operator places the insulation jacketed wire and terminal into a conventional ultrasonic welder, such that the bottom surface of the base rests upon the anvil and the insulation jacketed wire is aligned with the tip. The operator then causes the sonic welder to automatically sequence to weld the wire to the terminal through the insulation of the wire. Considerations include, there must be a displacement volume for the melted insulation jacket to go to; the insulation jacket must be of a composition which melts when heated so that it will flowably displace, as for example thermoplastics; and the thinner the insulation jacket the better, particularly in terms of accommodating insulation jacket dissipation mass.
Examples of the method of UWTI were presented in the disclosure of application Ser. No. 09/993,797, as follows.
Three insulation jacketed wires were tested as indicated by Table I. Insulation jacketed wires having I.D. numbers 1 and 2 are a seven strand copper wire with an ultra thin wall PVC insulation jacket 0.25 mm thick. Insulation jacketed wire having I.D. number 3 is composed a solid core copper wire with an ultra thin wall PVC insulation jacket 0.25 mm thick. In each case the terminal was of a copper alloy. The ultrasonic welder was an “Ultraweld® 40” ultrasonic welder of AMTECH® (American Technology, Inc.) of Milford, Conn. operating at 40 kHz, having anvil and tip cross-sections of 2.1 mm by 2.1 mm. In each example an excellent ultrasonic bond was achieved between the wire and the terminal, in terms both of strength and electrical conductivity.
TABLE IThicknessThicknessI.D.Wire SizeEnergy1st ContactWeld ContactAmplitudeBefore WeldAfter WeldNo.(mm2)(Joules)Pressure (psi)Pressure (psi)(microns)(mm)(mm)10.35 (22 gauge)312328251.660.732 0.5 (20 gauge)343033271.801.0030.14 (26 gauge)131821201.420.81
Advantages of the UWTI technology include improved electrical stability between the wire and the terminal, ability to construct multiple wiring subassemblies of complex wiring assemblies, and ability to utilize small gauge wires (smaller than 26 gauge, as for example 22 gauge and smaller) because the delicate wires are not subject to a stripping step which tends to damage them.
What remains needed in the art is to somehow incorporate UWTI technology into an electrical connector.